20reps of HS wall walks? as in 20 reps of walking up and down the wall to HS from pushup position or just hand touches on the floor?
4x2 ring HSPU. sure, whatever works.
Day 3: probably not enough volume, remotely. How long can you hold a ring handstand for with good form? You can hold a ring support for 60s easy, right?
Straight arm presses?
I'd start working the press downs against the wall. 10-15 reps total. break it up as you see fit. 2-5r a piece. hands further away from the wall makes it easier but you must turn out hands or turn towards an undergrip or it will kill your wrists. you can also try on parallettes.
I would the negative press to a point where you could hold as low as you can go for 5s. however, if you do so, you won't be able to do as many presses in a row. you can try to explore and see how low you can lower to and press up to; but I think doing the negative press and just jumping back to HS against the wall would be better for a start.
Headstand presses in straddle and pike should be mastered first. these should be very easy I would think. You can then start on bent arm HS presses against the wall.
You may be able to work press HS and ring HS. This is something you'll have to figure out how much volume you can do but may be doable.